Engine Dieseling - Options?

-
I never try to set the air screws the "same". That's just not the right way. You adjust with the vacuum gauge. Get each one to the highest reading on the vacuum gauge, in gear if an auto and then one half turn leaner. "Wherever" they end up is where they are supposed to be after that. That's how it's always worked best for me.
 
RustyRatRod said:
I never try to set the air screws the "same". That's just not the right way. You adjust with the vacuum gauge. Get each one to the highest reading on the vacuum gauge, in gear if an auto and then one half turn leaner. "Wherever" they end up is where they are supposed to be after that. That's how it's always worked best for me.
Click to expand...
Same here. Never had a single problem with it.
 
33IMP said:
Shut it off in gear, with your foot on the brake.


I cant believe some other smartass didnt beat me to it.
Click to expand...
You fool, not like that, you shut it off in gear with the parking brake set.
I thought every one knew that. LOL
 
billsdartgt said:
I was able to do a little check tonight - got the engine warm and checked for vacuum leaks - nothing shows up any where - good and bad I guess but will eliminate that as an issue - next I backed everything off on the carb, mixture screws front to 3/4 and rears to a 1/4, idle screw backed off completely, reset timing to 20 - idle down to around 900, vacuum now moving between 7 and 9, not jumpy or fluttering though. heavy rpm drop when going into gear, exhaust smells a little rich still - dieseling was nearly gone, cranking still ok with no kickback. Looks like I will find a decent spot for initial from 16 to 20, so looks like Im heading in the right direction, I would be OK driving as is to go top off the gas tank and finish diluting the octane boost juice down. starting to hope again I can tune out and run on pump gas - Im gonna get back at it this weekend, first thing is the carb is coming off for a good thorough inspection if I can get a rebuild kit with all the gaskets, may even re-jet my 670 and put in on there - it has been a proven performer on my Mustang - thanks for all the info - will see what I can do with a little refresh of thinking
Click to expand...
Glad to hear you are making progress.
LIke I mentioned before this is a balancing act with the idle mixture screws and timing dont get frustrated take baby steps in the process and you will get it.
Like Rusty said use a vacuum gauge to set the mixture screws - SLOWLY.
There is most likely nothing wrong with your carb gutting it know is just going to throw a curve in your tuning process. I would work with what you got.
 
RustyRatRod said:
I never try to set the air screws the "same". That's just not the right way. You adjust with the vacuum gauge. Get each one to the highest reading on the vacuum gauge, in gear if an auto and then one half turn leaner. "Wherever" they end up is where they are supposed to be after that. That's how it's always worked best for me.
Click to expand...
Well yeah, I didn't mean to say you just make them the same for the sake of making them the same but they should end up close on a 4-corner carb ....I shoulda been more clear. But,1/4 turn out on the secondary and 1/2 on the front tells me something's not right.
 
Somehow I read it that you have 11.5 to 1 compression. Then I reread and notice it's probably 10.5 to 1...
I retract my initial diagnosis after rereading and agree that it's likely not an octane issue but the tuning issue..
"Assuming" you have the correct torque converter.. but that much duration in your cam it's going to sound super cool idling at 900 or 850... But it's not good for it..
 
billsdartgt said:
I was able to do a little check tonight - got the engine warm and checked for vacuum leaks - nothing shows up any where - good and bad I guess but will eliminate that as an issue - next I backed everything off on the carb, mixture screws front to 3/4 and rears to a 1/4, idle screw backed off completely, reset timing to 20 - idle down to around 900, vacuum now moving between 7 and 9, not jumpy or fluttering though. heavy rpm drop when going into gear, exhaust smells a little rich still - dieseling was nearly gone, cranking still ok with no kickback. Looks like I will find a decent spot for initial from 16 to 20, so looks like Im heading in the right direction, I would be OK driving as is to go top off the gas tank and finish diluting the octane boost juice down. starting to hope again I can tune out and run on pump gas - Im gonna get back at it this weekend, first thing is the carb is coming off for a good thorough inspection if I can get a rebuild kit with all the gaskets, may even re-jet my 670 and put in on there - it has been a proven performer on my Mustang - thanks for all the info - will see what I can do with a little refresh of thinking
Click to expand...


When you get it right, the RPM drop should be no more than 150 RPM from neutral to in gear.

Usually when you see a big drop like that, the curve in the distributor is wrong. Once you clean that up, you’ll probably have to take some fuel away at idle.
 
billsdartgt said:
I think I have figure out the source of my woes but over the years have realized that once you peak at frustration its often easy to overlook some of what you know is right so I thought I would share some of my source of frustration to see if I have overlooked anything.

my engine (to start)

Static and Dynamic Compression numbers were from a few internet site calculations and some comments here on the board

72 360 block - bored .030 over
pistons - confirmed TRW 11.5-1 (probably shaved some)
CC volume of cylinder calced out @ - 5
Head volume calced out @ 69cc's
Static compression came in @ 10.5ish
dynamic compression came in @ 8.3/8.4
Edelbrock airgap intake
Holley 750 DP with mech secondary's. (carb is stock now with 70-MJ and 80SJ and 6.5 PV)
Plugs Autolite AP66
Comp Cam - 247/254 @ 508 int/exh lift 108 lobe separation - cam degreed in at 106 ICL
Doug's long tubes
engine has pretty stable 9" vacuum
idle 1150/1200 (lose about 150/175ish in gear)

Currently have distributer set with the FBO plate locked at 12 degrees of mech timing, moved from 12 initial up to as much as 22 initial - still searching for the sweet spot - with full charged battery no issue on starting at 20 degrees initial - may be good at 22, but most happy at 18

Ok, do you have the advance locked out? If you do, I don’t understand these numbers.

If the advance isn’t locked, then just as important as initial is, the curve is equally important.

Just trying to get a handle on what the distributor is doing.



I started the engine back around labor day - broke the cam in, changed the oil, pulled and cleaned plugs - engine sounds awesome - feels strong under the foot on the accelerator - had a few issues with brakes, alternator charging, etc. but the main issue is the engine dieseling when shutting down, still a few other issues to deal with once I get the engine where I feel good about hitting the street with it.

What ive done:

I tore the carb apart to confirm clean and what the jets were, primary was actually 73s, they were changed to the 70s that were listed as stock on Holley website, didn't try to confirm, measure, or change anything else

added fuel regulator to be able to make sure what fuel pressure was and no spikes

confirmed T slot exposure with carb off and set appropriately - no adjustment made after installed

changed to colder autolite 3923 plugs

added 6-8 ouces of octane boost (royal purple) just over 1/2 tank according to gauge - after adding the heavy dieseling slowed down a bit, moved the initial back to 20, car seem to like 18 as the best - easy start and idles good there - its a little rich and didn't try any adjustments

checked cylinder pressures engine slightly warm, all plugs out and carb open all the way through the plates - first few were 210 - 220 range - Not too bad I said to myself, realized battery was down on charge - after some quick charging - rechecked a few cylinders, looks like Im gonna be in the 225 to 235 range on all 8, stopped to let the battery fully changed and to get over frustration before setting the car on fire

My conclusion is that my dynamic numbers are off and I just need some higher octane fuel to run the engine, I have a preliminary thought on how to achieve but want to see if perhaps I could also tweak something, adjust something, or almost anything that I don't have to go and spend an assload of money on, I reran all my numbers on the same websites I got my original numbers from and it looks like if I could get 72 - 73 cc's on the head that could drop the dynamic down closer to 8 - does it look like Im heading in the right direction?

(this is by far my most long winded post i ever did - and Tim I would have sent this straight to you but your inbox is full LOL.)

I could have missed something I did or tried, hope the post isn't to hard of a read
Click to expand...
 
@yellow rose - Tim, I installed the FBO plate at 12, all in timing with initial gives me 32 degrees total, also checked at 20 degrees initial the advance starts around 23/2400, all in by 2800, checked lower initial and the all in still just adds the 12 limited by the FBO plate

regarding the torque convertor, plans are to eventually get something suited for the cam in the 2800/3000 range, I do not know what is in there right now though,

regarding the idle screws - I chocked them down as noted earlier, car is still rich, and since I juiced it I can tell the juice is mixed enough to become part of the fuel hitting the carb, its part of the exhaust smell richness - to me something is off with the carb as most here have mentioned it needs tuning, however even choking the idle screws almost shut its still pulling the fuel - Saturday morning will start a fresh set of rechecks, and as mentioned I may put the 670 I have on, I know it to be fully functional and responsive to adjustments - at least if I have a similar issue I can also eliminate strictly a carb issue.

@jpar - yes the car did measure out to have roughly 10.5-1 static compression, the pistons per their part number they are the TRW 11.5-1 pistons though.

aggravating shiznit for sure LOL - all the comments are appreciated
 
billsdartgt said:
@yellow rose - Tim, I installed the FBO plate at 12, all in timing with initial gives me 32 degrees total, also checked at 20 degrees initial the advance starts around 23/2400, all in by 2800, checked lower initial and the all in still just adds the 12 limited by the FBO plate

regarding the torque convertor, plans are to eventually get something suited for the cam in the 2800/3000 range, I do not know what is in there right now though,

regarding the idle screws - I chocked them down as noted earlier, car is still rich, and since I juiced it I can tell the juice is mixed enough to become part of the fuel hitting the carb, its part of the exhaust smell richness - to me something is off with the carb as most here have mentioned it needs tuning, however even choking the idle screws almost shut its still pulling the fuel - Saturday morning will start a fresh set of rechecks, and as mentioned I may put the 670 I have on, I know it to be fully functional and responsive to adjustments - at least if I have a similar issue I can also eliminate strictly a carb issue.

@jpar - yes the car did measure out to have roughly 10.5-1 static compression, the pistons per their part number they are the TRW 11.5-1 pistons though.

aggravating shiznit for sure LOL - all the comments are appreciated
Click to expand...
If you added a couple gallons of race fuel would that hurt anything?.. again your local Baxter's will have five gallon cans of it and that's the hard part cuz it's expensive there. Pour 2 gallons in of the can swish it around and take it for a good ten mile drive.. come back and watch it turn right off..
personally you could run it as rich as you wanted to in my opinion and if it doesn't have spark how's it going to ignite? The extra Rich fuel would be cooling the cylinder... The 11 to 1 Pistons are only 11 to 1 assuming a certain combustion chamber size...
I'm not quite sure how Pistons can make that claim..
There's no question you need for things to make your car run, air, fuel, spark, compression... I'll have to go back to the first post and see what plugs are using and calling cold... Are they just colored more than three threads from the bottom?... did I remember correctly you had 220 to 240 cranking pressure?..
 
billsdartgt said:
@yellow rose - Tim, I installed the FBO plate at 12, all in timing with initial gives me 32 degrees total, also checked at 20 degrees initial the advance starts around 23/2400, all in by 2800, checked lower initial and the all in still just adds the 12 limited by the FBO plate

regarding the torque convertor, plans are to eventually get something suited for the cam in the 2800/3000 range, I do not know what is in there right now though,

regarding the idle screws - I chocked them down as noted earlier, car is still rich, and since I juiced it I can tell the juice is mixed enough to become part of the fuel hitting the carb, its part of the exhaust smell richness - to me something is off with the carb as most here have mentioned it needs tuning, however even choking the idle screws almost shut its still pulling the fuel - Saturday morning will start a fresh set of rechecks, and as mentioned I may put the 670 I have on, I know it to be fully functional and responsive to adjustments - at least if I have a similar issue I can also eliminate strictly a carb issue.

@jpar - yes the car did measure out to have roughly 10.5-1 static compression, the pistons per their part number they are the TRW 11.5-1 pistons though.

aggravating shiznit for sure LOL - all the comments are appreciated
Click to expand...

Have you checked cylinder pressure? What is it?
 
Something is wrong somewhere. You say is has 220-240 PSI, yet the engine wants timing like it's a 7.5:1 motor. I'd be rechecking some things. There's no way in the world it will want that much timing with such great cylinder pressure. You sure it wasn't 120-140?
 
I'm not following your calculations for compression...
11 to 1 Pistons don't make any sense to me... Unless they're saying that is at zero Deck with x cylinder head CC...
 
RustyRatRod said:
Something is wrong somewhere. You say is has 220-240 PSI, yet the engine wants timing like it's a 7.5:1 motor. I'd be rechecking some things. There's no way in the world it will want that much timing with such great cylinder pressure. You sure it wasn't 120-140?
Click to expand...
I think it's compression is much higher especially if it's wanting that much initial timing. And who would put together a motor with that cam with low compression...
 
j par said:
I think it's compression is much higher especially if it's wanting that much initial timing. And who would put together a motor with that cam with low compression...
Click to expand...

Low compression engines demand less timing. High compression engines don't need a lot. His problem is the reverse of what it would be with too much compression.

Now, if perhaps he had a 383 distributor in it and it was spinning backwards, that might explain it. I've seen that one first hand.
 
numbers are correct - 220-230ish - I never had an engine with that high of numbers, hoping it means the rings are good LOL
well I got back at the car this weekend, worked on my brakes, even if I could get the car happy running wise they weren't good enough to get out of the driveway with. I started off as I mentioned with my 670, re-jetted, rechecked everything just to be sure no issues from the last time I ran it, even checked the PV, went step by step on the install trying to make sure I paid attention to every detail for the install, even reset the kick down 100% properly, I only thought I set it right the first time, at least it is much closer. So after I get everything installed and start it up, try to kick down off the high idle from the choke - nothing doing - same sh*t as before - DAMN - I know this carb is good - so I do a little checking, I found my culprit, of course he had an installer who is partly to blame

IMG_0595.JPG
not sure when I set the throttle on the 750 but quite sure I set it up the same way, when I locked the cable down it was with the carb sitting in the choke position, so I basically locked the throttle open to high idle, the transfer slot exposed as a result was a source of the pain and suffering - right now car is at 850ish on idle with 22 degrees initial timing - no dieseling or kickback and no start issues - Go figure - since I have the 750 off I am going to take it apart anyway to recheck everything including the PV, once all checked I will put it back on and see how it does. right now I will be able to hit the streets for the first time since October last year when I started out to check some freeze plugs and strut rod bushings - what a run of crap, may get a better sense of what PV the 750 may like when Im out on the street with the 670, maybe
 
Wow. What is the @.050 numbers on your cam? That is a TON of cranking compression. Unless that cam is incredibly small at .050 it must be 8 degrees advanced.
 
yellow rose said:
Wow. What is the @.050 numbers on your cam? That is a TON of cranking compression. Unless that cam is incredibly small at .050 it must be 8 degrees advanced.
Click to expand...
One tooth off on the timing set? Or maybe a misinterpretation of a multi keyway set.
Ive only had one engine that ever had that much cranking pressure, an oil burning, worn out 396 chevy. It had a whole bunch of flat cam lobes.
 
33IMP said:
One tooth off on the timing set? Or maybe a misinterpretation of a multi keyway set.
Ive only had one engine that ever had that much cranking pressure, an oil burning, worn out 396 chevy. It had a whole bunch of flat cam lobes.
Click to expand...
You had one too eh? I had (for a very short time) a '69 Chevelle 396 4 speed with 220+ compression in each cylinder and it would kill mosquitos for miles around! That thing had such bad valve seals that it would oil foul plugs in 100 miles. Rings were fine, did a leak down test and it passed with flying colors. I was glad someone made me an offer for the car that I just couldn't refuse.
 
247/254 @ .050 - 108 lobe separation, 508 lift intake/exhaust - cam had 4 degrees built in, I installed retarded it so it would have 2 degrees, changed the ICL from 104 per the cam card to 106 per the mgi speedware website - cam was degreed in - will see how it does next weekend, if the valves don't rattle I will be OK for now
 
You must log in or register to reply here.
-

Back
Top